The subject matter disclosed herein relates generally to mineral extraction and, more particularly, to a system and method for removing minerals from a brine using electrodialysis.
There are several regions in the United States (e.g., the southwestern United States including New Mexico, Southern California, and parts of Texas) and throughout the world that experience shortages in potable water supplies due, in part, to the arid climate of these geographic locales. As water supplies are limited, the need for innovative technologies and alternative water supplies for both drinking water and agriculture is important. One method for obtaining an alternative source of potable water uses desalination systems to produce the potable water.
The desalination process involves the removal of salts from seawater, agricultural run-off water, and/or brackish ground water brines to produce potable water. Desalination may use an assortment of filtration methods, such as nanofiltration and reverse osmosis, to separate the raw stream into a desalinated water stream and a tailing stream. The tailing streams may contain various salts and other materials left over after the desalination process. Indeed, disposal of the tailing streams produced by desalination may result in soil degradation and ground water contamination. Thus, alternative and innovative uses of the tailing streams may reduce undesirable results of disposing the tailing streams.
One such alternative use involves processing the tailing stream to remove valuable minerals. In particular, inland brackish water and seawater may be rich in sulfates, magnesium, calcium, and other minerals. Sulfates, mainly in the form of gypsum, have a variety of commercial uses, including, but not limited to building materials (e.g., drywall or sheetrock), skin creams, shampoos, and dental impression plasters. In addition, gypsum may be used as a fertilizer and/or soil conditioner in the farming industry. Magnesium may also be extracted in the form of magnesia (e.g., magnesium oxide) which is used in the refractory industry due to its fireproofing capabilities as well as in the medical field as an ingredient in laxatives. As the traditional deposits for these minerals are depleted, the capacity to extract them from alternative sources represents both a valuable commercial opportunity as well as a means for lessening the environmental impact caused by the disposal of waste streams high in salt content.
Existing procedures for the removal of minerals often exhibits sub-optimal efficiency. For example, evaporation pools require a large area of land and often produce low purity mixed salts with minimal commercial value. In addition, a waste mixed salt solid resulting from the evaporation process may leach into the ground water supply. Other methods of extraction involve processing the tailing stream produced in brackish water or seawater desalination plants. However, current mineral extraction procedures for the tailing stream may not operate efficiently.
As described above, desalination systems may employ one or a combination of nanofiltration and reverse osmosis to facilitate the desalination and removal process. Following an initial separation of a potable water stream from a tailing stream, the tailing stream may be processed further by a mineral removal system. For example, various precipitation techniques may be performed that facilitate removal of dissolved minerals from a solution. However, the high salt concentration in the tailing stream may increase the solubility of many of these valuable minerals and, as a consequence, decrease the efficiency in which these minerals may be precipitated. Inadequate removal of these minerals may have a negative impact on the mineral removal system itself. For example, incomplete gypsum removal may result in scaling of filtration and/or reverse osmosis membranes, thereby reducing the life and permeate flux of these membranes. Frequent replacement and repair of such mineral removal system components, in addition to the sub-optimal extraction efficiency, may result in elevated cost of mineral removal prompting the need for further optimization of the mineral removal system.
Furthermore, existing procedures may be inadequate to remove impurities from minerals. The ineffective removal of such impurities, including arsenic, boric acid, and silica, may result in undesirable impurities in removed minerals and decreased productivity of the mineral removal plant due to membrane scaling. Thus, an improved mineral removal system may facilitate higher purity of valuable minerals, decrease impurities, increase efficiency, and increase the life-span of components of the mineral removal system.